This relates generally to optical polarizers and, more particularly, to polarizers in the displays of electronic devices.
Electronic devices often have displays such as liquid crystal displays and organic light-emitting-diode displays. Displays such as these often use polarizers. For example, a liquid crystal display may have upper and lower polarizers. Pixels in a liquid crystal display may be controlled to locally adjust the polarization of liquid crystal material interposed between the upper and lower polarizers, thereby creating images on the liquid crystal display. Organic light-emitting-diode displays have pixels that emit light. Circular polarizers can be included in displays such as organic light-emitting-diode displays to help reduce unwanted reflections from metal electrode lines within the display.
Linear polarizers are often formed from stretched polyvinyl alcohol (PVA) films doped with iodine. The stretched films contain iodine molecules that are aligned along the stretch axis of the PVA film. Light having its electric field oriented along the stretch axis tends to be absorbed by the PVA film, whereas light having its electric field perpendicular to the stretch axis is typically transmitted through the film. This non-uniform behavior causes light that is passing through the PVA film to become linearly polarized.
Polarizer films such as PVA films can be fragile and sensitive to moisture. To prevent damage to the PVA film in a linear polarizer, the upper and lower surfaces of the PVA film are typically covered with opposing upper and lower layers of tri-acetyl cellulose (TAC) material. In many devices, a rigid display cover glass layer is mounted over a polarizer to prevent damage to the TAC and PVA layers.
The inclusion of the rigid display cover glass can add undesirable weight to an electronic device. The cover glass can be omitted to reduce the size and weight of a device, but omitting the cover glass can make the polarizer and the display susceptible to damage from scratches.
Polarizers formed from PVA and TAC films can also sometimes exhibit undesirable surface roughness, leading to visual artifacts on a display.
It would therefore be desirable to be able to provide improved polarizers and displays for electronic devices.